During the production of concrete blocks, it is known inter alia to make use of a mould which is vibrated by means of vibrators during and/or after being filled with damp concrete mortar, the vibrators acting on the side walls of the mould. In this case, the vibrators used are imbalance exciters, which necessitate a complicated and a voluminous construction and are highly susceptible to wear at high vibration frequencies.
A large number of designs of linear motors are known in which linear motor coils and an armature moved by the latter are provided but, as a rule, roller bearings are used for the armature, cf. U.S. Pat. No. 4,868,431. Such linear motors are designed for large strokes of the armature. Apart from the fact that mountings of this type only permit a movement of the armature in a predetermined direction, for high stroke frequencies at small strokes, such as are needed in the case of vibrators, roller mountings of this type are unsuitable since, because of the mass moment of inertia, the rollers then cannot follow the movement of the armature, so that the result is quickly correspondingly high wear because of the lack of lubrication.
The use of ball bearings, as they are described in the German Patent No. 953 890, or sliding bearings, as they are described in WO 91/17874, leads to corresponding problems.